Local resident Jack Reece said he witnessed one of the fires being started on Sunday evening and contacted emergency services.

“I could see flames up to eight feet high in the distance. As I got closer, I could see a bunch of young people with a petrol container starting fires," he said.

“The fire service told me they are concerned as they are using petrol and petrol and children don’t mix well.”

Mr Reece said he was concerned that the castle was being "plagued" by arsonists.

Alerts have been issued to residents and police said they will be visiting high schools to highlight the problem.

The North Wales Arson Reduction Team said it had met with police.

Kevin Jones, arson reduction team manager, said: “Deliberate fire-setting incidents put extra pressure on fire and rescue resources and place crews and the public at extra risk.

“Whilst crews are busy dealing with these incidents, they would not be able to meet what may be a real need for them to attend a life-threatening situation elsewhere in the county.

“Deliberate fires are a serious form of anti-social behaviour with potentially lethal consequences and we are working closely with the police and other partner agencies in the area to try and tackle the problem.

“I would appeal to anyone with information on such activities to report it to North Wales Police on 101 or anonymously via Crime stoppers on 0800 555 111.”

A North Wales Police spokesman said they had a report around 6.30pm on Saturday of youths lighting a fire in the grounds of the castle.

He said: "Police found some burnt bits of windfall branches but no damage and no damage to trees. Reported as anti–social behaviour."